The present invention relates to roller conveyors. Conventional roller conveyors employ a series of rollers mounted between two sides of a frame. The rollers are driven to convey objects along the length of the conveyor.
In some instances, it is necessary or desirable to have the rollers as close together as possible. This is especially important when conveying objects which are small, unevenly shaped, fragile, or otherwise difficult to handle. For example, when pallet loads are stacked on pallets having spaced boards running parallel to the rollers, the rollers must be positioned sufficiently close together to prevent the boards from lodging between the rollers. Similarly, when the load includes a group of small objects stacked in columns, the rollers must be positioned sufficiently close together to prevent the small objects from falling between the rollers.
In some instances, it is necessary or desirable to drive each roller in a series of closely spaced rollers. This eliminates nip points and is especially important when the objects being conveyed are small, when the objects are covered with packaging or include loose parts, or when it is necessary to provide additional protection against having the rollers seize and injure the fingers of personnel.
In such instances, the lack of space between the rollers and the need to drive each roller presents constraints on designing economical drive mechanisms which are durable and supply sufficient torque to power the series of rollers.
One way of mounting rollers on a conveyor frame is to use rollers which have narrow shafts fixed to each end. The narrow shafts are supported by the inner races of bearings, and the outer races of the bearings are fixed to the frame. The rollers can be driven by driving the shafts. The narrow shafts allow room for sprockets and permit the rollers to be closely spaced with every roller driven. However, this mounting arrangement is significantly more expensive than other mounting arrangements.
A less expensive arrangement involves mounting the outer races of bearings inside the rollers, mounting the inner races of the bearings on axles and fixing the axles to a frame. While this arrangement is much less expensive, the rollers cannot be driven by driving the axles. Rather it is necessary to drive the rollers by driving the roller surfaces directly, or by driving an element attached to the outer circumferential surface of the rollers or the axial ends of the rollers.
Attaching drive sprockets to the outer circumferential surface of the rollers is a relatively inexpensive procedure which provides the rollers with a durable mechanism for receiving and supplying high levels of torque. However, it places severe limitations on the positioning of the drive train and how closely it is possible to space a series of rollers in which every roller is driven.
It is possible to use drive sprockets attached to the outer circumferential surface of the rollers and drive every roller in a series of closely spaced rollers. However, to do so, it has been necessary to stagger the axial ends of neighboring rollers on both sides of the conveyor, mount the drive sprockets on the end portions of the outer circumferential surfaces of the rollers on both sides of the conveyor, have the drive train drive every other roller along one side of the conveyor, use one of these rollers to transmit power to the other side of the conveyor and continue the drive train along the other side of the conveyor, driving every other roller on that other side of the conveyor.
Having the externally mounted sprockets of the power train start along one side of the conveyor and continue along the other side of the conveyor causes difficulties in loading and unloading products from the side of the conveyor. Since the sprockets extend substantially above the conveying surface of the series of rollers on both sides of the conveyor, they interfere with loading and unloading products from both sides of the conveyor. This makes the use of a forklift substantially more difficult and time consuming, and increases the likelihood of damaging the conveyor components while using a forklift.
One way to avoid such interference on the side of the conveyor is to attach gears to the axial ends of the rollers at one side of the conveyor and connect the gears with idler gears to form a drive train. However, this arrangement is much more expensive and requires much greater precision than the other arrangements described.
A wide variety of arrangements have been used to support, journal, and drive the rollers on conventional roller conveyors. However, none of the conventional roller conveyors provide an apparatus which is economical to build, durable in operation and capable of supplying sufficient torque, when the rollers need to be closely spaced with every roller driven and when it is necessary to have no conveyor components above the conveying surface of the series of rollers on one side of the conveyor which interfere with loading and unloading the conveyor.